1. Field of the Invention
The present invention relates to a sheet feeding apparatus such as recording paper feeding apparatus and intermediate tray of a copying machine for both side of paper for feeding one sheet each by separating from a stacked state of sheets, regardless of the sheet size, when sheets of single-form documents or recording paper are used in plural sizes in a copying machine or the like.
2. Description of the Prior Art
In a copying machine equipped with a recirculating document handler (RDH) for stacking up documents of single form in a plurality, separating and feeding the documents one by one from the top side or bottom side, and returning to the stacked position after reading the documents in the bottom side or top side, a sheet feeder is used, such as the feeding apparatus of documents and the feeding apparatus of separating and feeding the stacked recording sheets one by one. In printing apparatus and photographic printing device, too, an apparatus for separating and feeding stacked recording papers is employed. In such paper feeding device, it is necessary to separate the stacked sheets one by one, and various separating methods are known, such as the air flow separating method, separating claw method, and method for separating sheets by using a roller rotating in a reverse direction of sheet feeding direction.
As an example of the prior art of separating sheets by using air flow, "the sheet feeding apparatus" is disclosed in the Japanese Laid-open Patent No. 58-78932, and a similar structure is found in the U.S. Pat. No. 3,198,514 or the Japanese Patent Publication No. 55-19859. The structure is shown in FIG. 1, a side view, and in FIG. 2, a plan view. This composition is, for example in a copying machine of RDH method, a paper feeding 1 for feeding by separating the stacked recording papers one by one. The paper feeder 1 is provided with a support tray 3 on which recording papers 2 are stacked up.
At the downstream side of the feeding direction A1 of the recording paper 2 and near the middle of the widthwise direction of the support tray 3 intersecting with the feeding direction A1, a notch 4 is formed, and a feed belt 7 stretched on a pair of rotating rollers 5, 6 disposed beneath the support tray 3 and having many penetration holes formed is exposed at this notch 4. Between the rotating rollers 5, 6 is arranged an air intake duct 8 opposite the notch 4 across the feed belt 7, and the recording paper 2 on the support tray 3 is attracted by vacuum to the feed belt 7, and is fed in the feeding direction A1 by running and driving of the feed belt 7.
On the other hand, since there is a possibility that plural recording papers 2 on the support tray 3 be attracted and fed together by the feed belt 7, an air injection duct 9 is disposed above the downstream side of the feeding direction A1 from the support tray 3, and nozzles 10b to 10e parallel to the feeding direction A1, and plural nozzles 10a, 10f directed toward the middle of the widthwise direction are communicated. On the other hand, the support tray 3 has a base part 5 in an extended shape from the downstream side to the upstream side of the feeding direction A1, and a side wing parts 15, 16 formed obliquely upward from the both sides of the widthwise direction of the base part 14, as shown in FIG. 3
The air injection duct 9 and support tray 3 in this prior art are arranged as shown in FIG. 1, and the air stream in a flat shape is concentrated near the middle position in the widthwise direction of the support tray 3 by the nozzles 10a to 10f. This state of distribution of air stream by the air injection duct 9 is indicated in the shaded area in FIG. 4.
This prior art is capable of separating the recording papers 2 favorable as far as the size of the recording papers 2 is relatively small or the weight is relatively large.
However, in the case of recording paper of relatively large size or small weight, or therefore in the case of recording paper of weak consistency, favorable separation may not be always possible. That is, in this prior art, by concentrating the air stream near the middle portion of the widthwise direction of the support tray 3, the air stream is inflated in the vertical direction near the middle position to realize the action of separating the recording papers. On the other hand, in the recording paper of large size or small weight, not only the lowermost recording paper but also plural recording papers are deformed with a relatively large deflection, in a recess 19 formed by the base part 15 and side wing parts 15, 16 of the support tray 3, in a shape corresponding to the pattern of the recess, and the gap for entry of air stream is hardly formed among the recording papers, and separation of recording papers may be sometimes unsuccessful.
Or among the recording papers indicated in the shaded area in FIG. 4, the area of separation region 17 mutually separated by entry of air from the air injection duct 9 becomes relatively smaller than the area of the non-separating region 18 where the recording papers adhere with each other, and therefore when the lowermost recording paper is attracted in vacuum by the conveying belt 7 and conveyed, duplicate feed may occur due to the frictional force in the non-separating region 18. At this time, in order to extend the separating region 17, when nozzles 10g, 10h indicated by double point chain line in FIG. 2 are disposed further outward in the widthwise direction of the nozzles 10a, 10f in the air injection duct 9 so as to be directed outward in the widthwise direction, in the case of recording paper 2 of which width W1 is smaller than the interval L11 shown in FIG. 2 between the nozzles 10g, 10b, the air stream from the nozzles 10g, 10h collides against the both ends 2a, 2b in the widthwise direction of the recording paper, and these end parts 2a, 2b come to flap. In this case, the stacked state of the recording papers 2 piled up in the paper feeder 1 is disturbed, and duplicate feed or defective feed may take place. Or when the recording paper 2 is relatively small in size, the separation capacity due to the air stream concentrated by the nozzles 10a to 10f is excessive, and the recording papers of small size may scatter about in the paper feeder 1.
In the prior art, therefore, although the separating capacity is relatively favorable as far as the recording paper is limited in type, separation failure or feeding failure may occur from the viewpoint of versatility of separating recording papers in a wide variety of sizes effectively, and it is not sufficient in versatility, and the sheet feeding apparatus with versatility having the favorable separating capacity in a wide range of size and weight of recording paper is desired.
Usually, an electrophotographic apparatus such as copying machine and laser printer possesses a transfer unit composed of photosensitive material and transfer charger, and in this transfer unit, the image of the photosensitive material is transferred on one side of the recording paper contacting with the photosensitive material.
Incidentally when the recording paper is passed twice in the transfer unit so that the same side of the recording paper makes contact with the photosensitive material, a composite copy of obtaining an image synthesize on the same side of the recording paper is realized. On the other hand, when the recording paper is passed in the transfer unit so that one side and other side of the recording paper may contact with the photosensitive material sequentially, a two-sided copy of forming images on both sides of the recording paper is realized.
Generally, an electrophotographic apparatus capable of executing such composite copy or two-sided copy is equipped with a circulating route capable of transferring the recording paper repeatedly in the transfer unit, and this circulating route is composed of the transfer unit, conveying roller and other rollers, inverting claw, switchback part, and intermediate tray for temporarily storing the recording paper on which visible image is transferred on one side thereof. They interact to realize favorable composite copy or two-sided copy.
Such composite copy and two-sided copy are desired to be capable of performing plural times continuously for the sake of improving the working efficiency. Therefore, the intermediate tray is designed to store plural recording papers, and conventionally, in the paper feeding portion from the intermediate tray, the recording papers are taken out sequentially from the bottom side while blowing air and separating the recording papers.
In the conventional intermediate tray, however, when taking out the recording papers, scatter of recording paper due to air blow or defective biting into paper feed roller may occur.
More specifically, the recording paper conveyed in the circulation route is heated at the fixing unit in order to fix the image transferred in the transfer unit. At this time, the recording paper is often curled downward at the end portion due to massive heat, and the curved recording papers are stacked up on the intermediate tray. This curling will form a space between the recording papers and the intermediate tray, and this space may cause to scatter about the recording papers when air is blown in. This scattering of recording papers by air is particularly obvious when the number of recording papers is not enough to suppress this space by the own weight of the recording papers. Furthermore, the curling may cause defective biting such as folding at the curved part when held between the paper feed rollers.